Reference Centre, Genealogy 101
Answers to Genealogy FAQs - 7br, 8br, 9br, Xbr, 10br
The references are a sort of shorthand that had been used by court clerks and clerics, prior to the adoption of 1 January as the beginning of the New Year, in recording dates and are drawn in part from the Latin origins of cardinal numbers. The terms 7br, 8br, 9br and 10br, therefore, are counted from the old style New Year of March, thusly:
7br = septem (in Latin, cardinal number 7) + br (to represent 'ber') = September (in its expanded form and being the 7th month counted from and including March)
8br = octo (in Latin, cardinal number 8) + br = October (in its expanded form and being the 8th month counted from and including March)
9br = novem (in Latin, cardinal number 9) + br = November (in its expanded form and being the 9th month counted from and including March)
10br = decem (in Latin, cardinal number 10) + br = December (in its expanded form and being the 10th month counted from and including March)
Note that this sytem of shorthand notation for dates was never used for any of the other months of the year e.g. January, February, et cetera. This is attributable to the fact that none of the other months of a year represent numerals. Neither do the abbreviations ever appear without the added "br" for, even in the historical contemporary sense, the abbreviation for a month simply as the numeral "7" would not make sense and would have lead only to confusion.
The origin of the names of the months September through December definitely derives from the old Julian calendar (introduced by Julius Caesar) whereby the first month of the year was deemed to be March and, under that system, September was deemed to be the 7th month of the year.
I have grown so acquainted with these date abbreviations and what they signify that now, when I encounter them, I simply recite the Latin ordinal numbers to provide the name of the month i.e. septem, octo, novem, decem. No need to count the months to remember the expanded form of the abbreviation.